1. Field of the Invention
The present invention relates to a magnetic sensor capable of sensing a change in magnetic field with high sensitivity and a current sensor capable of sensing a change in current flowing through a conductor with high sensitivity.
2. Description of the Related Art
Generally, to accurately detect weak control current flowing through a circuit in control equipment, a method of connecting resistors in series in the circuit and measuring a voltage drop in the resistors is used. In this case, however, a load different from that of a control system is applied and there is the possibility that an adverse influence is exerted on the control system. Consequently, a method of performing indirect measurement by detecting the gradient of a current magnetic field generated by the control current is used. As a concrete example, there is a method of winding a line to be measured around a toroidal core, supplying control current to the line to be measured, and detecting a magnetic flux generated in the center portion of the toroidal core by a hall element.
With respect to a current sensor realizing the method, however, problems such as difficulty of realizing miniaturization and insufficient linearity or high frequency responsiveness are pointed out. To address the problems, a current sensor has been proposed in which a giant magnetoresistive element (hereinbelow, GMR element) producing giant magnetoresistive effect is disposed in the current magnetic field generated by control current and the gradient of the current magnetic field is detected (refer to, for example, U.S. Pat. No. 5,621,377). In relation to the current sensor, a technique of performing flaw detection on the surface of a metal substrate or the like by using a magnetic sensor having a GMR element is also disclosed. Such a magnetic sensor or a current sensor using such a GMR element has relatively improved detection sensitivity and responsiveness and obtains detection characteristics which are stable even the temperature changes.